Temperatures
Understanding Dough Temperature
When starting out with sourdough, it can be hard to understand why one bake turns out great, and the next bake not so much. Is it because of how mature my starter was, or how long the dough proofed? You start to look for magical connections or arbitrary factors, all to find reason in the madness...
Why are things not behaving in a consistent manner?
It's easy to give up due to a feeling of frustration and confusion whilst in this phase of your journey, and for me, managing my temperatures was a large piece of the puzzle.
So here I will try to help you make sense of one more factor you need to pay attention to when baking sourdough breads.
Impactors
What makes an impact on the temperature of your dough?
Anything that goes into the dough during the proofing process, as well as the dough surroundings, will influence the temperature, and hence the fermentation rate. So these days I am mindful of a few things:
The temperature of the air around the dough throughout the entire proofing period. Can be the room temperature or the temperature inside a proofing box.
If you store your flour in a cold room like me, know that it drags down the initial dough temperature. Measure it out the night before, especially in winter.
Water is usually the easiest variable to control, and it also has a disproportionate impact. Use it to your advantage:
Cool water to slow down the process in the summer and warm water to speed it up in the winter.
Any major component added during the bake contributes to the overall temperature.
Temperature is an ingredient in and of itself. Especially if you live in a place with seasons.
Control
Controlling temperature or time
Dough temperature can be measured with a probe thermometer. Just stick it in, take a reading, and based on this the proofing process can be adjusted to reach your target rise.
Or you can control the temperature, and keep the time constant. This is what I prefer, as it allows me to have a more consistent process, and I can plan my bakes around my life, rather than the other way around.
Controlling temperature
I have come to use a proofing box to control the environment around my dough, but I'm also particular about the water temperature, as it will have a big impact. As mentioned, I store my flour in an unheated room so usually I measure it out the night before and let it come up to room temperature before the bake. Especially in the winter.
Controlling time
If you don't control the temperature, you can instead adjust the time the dough is allowed to proof. Still, you should measure the temperature of the dough using a probe thermometer, and make sure you have an hour or so extra in your baking window.
If the dough is a few degrees below your target temperature, add a couple of folds to compensate. Check the rise, and verify.
Getting a feel for it
Regardless of which method you choose, I would recommend that you keep inspecting the dough. Look at it, feel it, and observe its appearance. This is how you build intuition, or get a feel for when the dough is ready.
Calculator
Let me do the maths for you…
All right, so science, right?
Scientists have measured how temperature drives fermentation, and based on their science I have built a calculator.
It lets you solve for whichever one out of the four you're after: starter percentage, time, temperature, or target rise. Slide the sliders for the other three, and it rearranges the same equation to fill in the fourth.
So you can bump up the sourdough to shorten the time in the winter, or lower the water temperature to do the opposite in the summer for example.
The constants
μ(Temp) is how fast the yeast and bacteria multiply. The warmer it is, the faster this happens.
That's the Ratkowsky bit, set by the lowest temperature they'll still grow at (T_min) and how steeply they speed up after that (b).
κ is just the head start your starter already gives you. So a bigger starter, or a warmer spot, both get you to your target rise sooner.
How it works
It's really two well-studied ideas put together. How fast the yeast and bacteria grow goes up with the temperature, which is the Ratkowsky square-root model1, tied to the temperatures Di Biase et al. actually measured for sourdough bacteria2.
So if the rise really is the time the yeast and bacteria in your dough needs to grow and multiply a certain amount, then the time to reach your target rise can be calculated based on this.
The table below lists the constants it relies on, and what each one does.
| Parameter | Value | What it represents |
|---|---|---|
| 2.4 °C | Minimum growth temperature of sourdough lactic acid bacteria | |
| 0.0276 | Ratkowsky square-root slope of the growth rate vs. temperature | |
| 0.195 | Scales the starter into the rise it has already “banked” |
References
- Ratkowsky, D. A., Olley, J., McMeekin, T. A., & Ball, A. (1982). Relationship Between Temperature and Growth Rate of Bacterial Cultures. Journal of Bacteriology, 149(1), 1–5. ↩
- Di Biase, M., Le Marc, Y., Bavaro, A. R., Lonigro, S. L., Verni, M., Postollec, F., & Valerio, F. (2022). Modeling of Growth and Organic Acid Kinetics … during Lactiplantibacillus plantarum ITM21B Fermentation in Liquid Sourdough. Foods, 11(23), 3942. PMC9741194 ↩